The present invention relates to new and useful surgical sutures and allied surgical products, and more particularly to strong but limp high compliance, monofilament sutures having unique handling and knot tying characteristics. The novel sutures and surgical products of the present invention comprise a sustantially oriented copolymer made from alkylene terephthalate and 2-alkenyl (or alkyl) succinate sequences.
U.S. Pat. No. 3,890,279 discloses molded articles made from copolymers of this invention having reasonable levels of crystallinity and flexibility as well as good tear strength. Molded articles made of material containing the copolymeric sequence described to this invention are also described in U.S. Pat. No. 3,891,604. From the teaching of these two patents, which relate to molded, practically unoriented articles, little can be predicted concerning the mechanical properties of highly oriented fibers made from these copolymers. Furthermore, U.S. Pat. No. 3,542,737, indicates explicitly that oriented multifilament yarns made from related copolymers, namely those containing ethylene terephthalate and 2-alkenyl succinate (0.5 to 15 mole %) sequences, display almost identical tensile properties when compared with the unmodified rigid yarn made from the high modulus parent homopolymer, polyethylene terephthalate.
Theory and experience in the art of fiber chemistry predict that branching--as present in the polymers described--may prohibit fiber formation and will exert a deleterious effect on the tensile properties of any resulting fibers by the inability of the unoriented branch to contribute to the load bearing capacity of the fiber, and by the steric interference posed by the branch to chain alignment during fiber orientation. It was therefore surprising that strong fibers, in particular strong, compliant "ultralimp" fibers may be formed from poly(tetramethylene terephthalate) copolymers with pendant hydrocarbon chains. Compliance is used in part to denote the reciprocal of modulus.
Many natural and synthetic materials are presently used as surgical sutures. These materials may be used as single filament strands, i.e., monofilament sutures, or as multifilament strands in a braided, twisted or other multifilament construction. Natural materials such as silk, cotton, linen, and the like, do not lend themselves to the fabrication of monofilament sutures and are accordingly generally used in one of the multifilament constructions.
Certain synthetic materials which are extruded in continuous lengths can be used in monofilament form. Common synthetic monofilament sutures include polypropylene, polyethylene and nylon. Such monofilament sutures are preferred by surgeons for many surgical applications due to their inherent smoothness and noncapillarity to body fluids.
Available synthetic monofilament sutures all suffer to greater or lesser degrees from one particular disadvantage, that is relative stiffness. Besides making the material more difficult to handle and use, suture stiffness or low compliance can adversely affect knot tying ability and knot security. It is because of the inherent stiffness of available monofilament sutures that many suture materials are braided or have other multifilament constructions with better handling, flexibility and conformity.
Most monofilament sutures of the prior art are also characterized by a low degree of compliance. This makes knot tying difficult and reduces knot security. In addition, the low compliance and limited ductility prevent the suture from "giving" as a newly sutured wound swells, with the result that the suture may place the wound tissue under greater tension than is desirable, and may even cause some tearing, cutting or necrosis of the tissue.
The problems associated with the use of low compliance sutures in certain applications were recognized in U.S. Pat. No. 3,454,011, where it was proposed to fabricate a surgical suture composed of Spandex polyurethane. Such sutures, however, were too elastic and did not find general acceptance in the medical profession.
Recently issued U.S. Pat. No. 4,224,946 describes a monofilament suture with good flexibility and knot strength, which suture is composed of block polyetheresters which contain (1) a polymeric block of polyalkene esters and (2) a polymeric block of aromatic dicarboxylic acids or cycloaliphatic acids with short chain aliphatic or cycloaliphatic diols.
It is an object of the present invention to provide a novel soft, limp, thermoplastic monofilament suture or ligature of poly[alkylene terephthalate-co(2-alkenyl or alkyl)succinate]. It is a further object of this invention to provide a monofilament suture with a desirable degree of ductility to accommodate changing wound conditions. It is another object of this invention to provide a monofilament suture with the flexibility and knot tying characteristics of a braided suture. It is another object of this invention to provide a new, nonabsorbable suture having a diameter of from about 0.01 to 1.0 mm and possessing unique and desirable physical properties. These and other objects will be made apparent from the ensuing description and claims.